High-precision variable radio frequency coil

ABSTRACT

A three turn coil cast in an epoxy casting which has on one end fine threads to accept a screw having a hole radially therein. In this hole is a compressed silicone rubber tension rod. A tuning core is bound to the screw with a silicone adhesive. A dummy material is also cast in the epoxy resin.

United States Patent Mazzochi et a1.

[ Oct. 9, 1973 HIGH-PRECISION VARIABLE RADIO FREQUENCY COIL Inventors: Roger W. Mazzochi, Bridgeport;

James A. Postlethwait, Fayetteville, both of N.Y.

The United States of America as represented by the Secretary of the Army, Washington, DC

Filed: Nov. 1, 1972 Appl. No.: 302,980

Assignee:

US. Cl 336/136, 336/192, 336/205 Int. Cl. 1101f 21/06 Field of Search 336/130, 136, 96,

References Cited UNITED STATES PATENTS 12/1965 Slenker 336/136 3,155,895 11/1964 Adams etal 336/136 X 2,318,415 5/1943 Patzschke et a1 336/136 3,259,862 7/1966 Richard 336/136 2,942,333 6/1960 Mason 336/136 X 2,552,999 5/1951 Pannell et al. 3361136 X 3,000,079 9/1961 Howell et a1 336/136 X FOREIGN PATENTS OR APPLICATIONS 629,195 0/1949 Great Britain 336/136 Primary Examiner-Thomas J. Kozma Att0rney--William G. Gapcynski et al.

[57] ABSTRACT A three turn coil cast in an epoxy casting which has on one end fine threads to accept a screw having a hole radially therein. In this hole is a compressed silicone rubber tension rod. A tuning core is bound to the screw with a silicone adhesive. A dummy material is also cast in the epoxy resin.

1 Claim, 2 Drawing Figures HIGH-PRECISION VARIABLE RADIO FREQUENCY COIL SUMMARY OF THE INVENTION A high-precision variable radio frequency coil formed by a solenoid wound three turn coil which is cast along with a dummy terminal in an epoxy casting. Leads from the coil protrude out from the epoxy casting along with the dummy terminal lead. The epoxy casting capsulates the coil and forms a circular section hole having one end portion extending through the coil and its other end portion having 80 threads per inch.

An 80 threads per inch polycarbonate plastic screw has a hole on one end in which a tuning slug is seated and attached thereto by a silicone adhesive. The use of this adhesive allows the coil to be at a minor misalignment with the center axis of the plastic screw and yet be able to align up with the portion of the hole in the casting which extends through the coil. At the other end of the screw is a slot which is designed to fit a standard electronic tuning wand or screwdriver. At the mid section of the screw a hole is machined completely through the diameter of the screw. A silicone rubber tension rod which is longer than the diameter of the screw is fitted into this hole. The rod is flexible in nature and is compressed similar to a compressed wire spring. The silicone rod will act as a tension device to resist, but not lock, the turning of the plastic screw.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic showing partially cut away of the preferred embodiment; and

FIG. 2 is a side view of the device shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIGS. 1 and 2 a high-precision variable radio frequency coil is shown. The assembly consists of a three turn coil 1 of 0.025 diameter wire. Coil 1 is solenoid wound with three turns right hand on a 0.032 diameter arbor, the arbor then being removed from the coil. A dummy terminal 6 is formed with a hook on one end.

The coil 1 and the hook portion of terminal 6 are cast in an epoxy casting 7. Casting 7 is formed with a circular section hole 3 therein having a smaller diameter portion projecting centrally through the coil 1 and a larger diameter portion coaxial therewith. The leads 9 and 10 of coil 1 protrude from this casting along with the dummy wire leads 6. The protruding leads are tinned to facilitate printed circuit board fabrication. The assembly may be directly inserted into a printed circuit board. The epoxy casting is in the shape of a cylinder having 0.30 inches diameter. The protruding end of terminal 6 is located 0.1 inches from the center of the epoxy casting 7. The larger diameter end of the hole 3 within casting 7 is provided with threads 12.

An 80 threads per inch threaded polycarbonate plastic screw 14 mates with threads 12. This screw affords a minimum amount of axial travel per turn of the screw. This is finer even than micrometer adjustment. The screw is approximately 0.130 inches long and is 0.160 inches in diameter. A small blind hole 16 is machined on one end surface. An inductance changing device or core 5 is formed of ferrite material with an initial permeability of 35 percent. The core or tuning slug 5 is 0.030 inches in diameter by 0.160 inches long. The

core is bonded to the plastic screw in the hole 16 by a silicone adhesive 17. By the use of a silicone adhesive and a hole 16 bigger in diameter, the core can be at a minor misalignment with the center axis of the plastic screw and still allow alignment through the hole 3 in casting 7. Of course, perfect alignment of the core is desirable but not necessary. At mid section of the screw 14 a radial hole 19 is machined completely through the diameter of the screw.

A silicone rubber tension rod 21 0.205 inches long is compressed into the hole 19. Rod 21 is flexible in nature and can be compressed similar to the compressing of a wire Spring. The rod 21 is inserted into the radial hole 19 and is longer in length than the diameter of the plastic screw. The silicone rod will act as a tension device to resist, but not lock, the turning of the plastic screw.

At the other end of the screw 14, a slot 23 is machined into the screw. The slot 23 is designed to fit a standard electronic tuning wand or screwdriver.

In the base casting of the epoxy resin a mold having a cavity of the size and shape shown in FIGS. 1 and 2 is prepared. The formed coil and dummy terminal wire are inserted into the mold and the mixed epoxy is poured. After the epoxy has hardened, the casting is removed from the mold. Internal threads 12 of threads per inch are formed when the casting is made. The center line of these threads are casted to the center line of the coil hole. This hole and threads will accept the plastic screw combination 14 without the necessity of having perfect center alignment of the coil, tuning slug, and plastic screw. This was made possible by the use of the silicone adhesive 17 when bonding the tuning core 5 to the plastic screw.

The assembly of plastic screw 14 with silicone tension rod 21 and bonded ferrite tuning core 5 is screwed into the epoxy coil casting 7. When the plastic screw is turned from a flush position (shown in FIG. 1) to full depth of penetration, an inductance change of approximately 8 nano Henries to 32 nano Henries is achieved. An average change of one nano Henry per two turns of the tuning screw 14 occurs at the minimum inductance range. An average change of 2.5 nano Henries per one turn occurs at mid inductance range and an average change of 3.5 nano Henries per one turn occurs at the maximum inductance range. The wide tuning range is achieved by the physical design of the base casting which allows the core to be adjusted fully out of the coil to fully inserted and by the electromagnetic characteristics of the core material selected, which affects a greater reduction in reluctance to the travel of the lines of flux. Values of Q (quality factor of coil) over the entire tuning range were held comparatively high (minimum value of 50). The dummy terminal 6 gives the assembly additional physical stability and strength, and allows the packaged coil to fit into a standard TO-S configuration for printed wire board applications.

We claim:

1. A variable inductor comprising a coil; a casting; said casting enclosing said coil; terminals connected to said coil extending through said casting; a movable core; said coil and casting have an opening in the middle of said coil which will accept said movable core; said casting forming internal threads which have a center line approximately equal to a center line of said coil; a screw means adaptedto mate with the threads of said casting; said core being joined to one end of said screw screw means having a radial hole drilled radially all the way through said screw; a silicone rubber tension rod of a length longer than the length of said radial hole; said tension rod being compressed into the radial hole in said screw means; and said screw means having a slot on the end opposite the end the core is attached to. 

1. A variable inductor comprising a coil; a casting; said casting enclosing said coil; terminals connected to said coil extending through said casting; a movable core; said coil and casting have an opening in the middle of said coil which will accept said movable core; said casting forming internal threads which have a center line approximately equal to a center line of said coil; a screw means adapted to mate with the threads of said casting; said core being joined to one end of said screw for movement thereby into and out of said Coil; a silicone adhesive; said screw means having an opening in one end in which said core is attached by means of said silicone adhesive; a dummy terminal having one end bent in a hook shape and embedded into said casting, and having another end protruding out from said casting; said casting being made from epoxy resin; said screw means being made of polycarbonate plastic; said screw means having a radial hole drilled radially all the way through said screw; a silicone rubber tension rod of a length longer than the length of said radial hole; said tension rod being compressed into the radial hole in said screw means; and said screw means having a slot on the end opposite the end the core is attached to. 